Evidence for host resistance in 1,3 bis(2-chloroethyl)-1-nitrosourea treatment induced in syngeneic LSA lymphoma

Characterization of T lymphocyte clones isolated from BCNU-cured LSA mice

1,3-Bis(chloroethyl)-1-nitrosourea (BCNU) has been shown to "cure" over 90% of the mice bearing the syngeneic tumor LSA, and the cured mice acquire elevated levels of tumor-specific immunity. In the present study, we report for the first time the establishment and characterization of several tumor-specific CD8+ cytotoxic T cell (CTL) clones from splenic T cells of BCNU-cured LSA mice. Many of these clones were found to be strongly cytotoxic to LSA but not to a different H-2b tumor target such as EL-4, or the natural killer (NK)-susceptible target YAC-1, NK-resistant target P815, or con A or LPS blasts from H-2b mice. Some of the clones showed a moderate level of cytotoxicity to the NK-susceptible target YAC-1. The relative roles of interleukins such as IL-2, IL-4 or IL-6 in supporting the proliferative response of some LSA-activated CTL clones were analyzed. As expected, recombinant human (rh) IL-2 alone supported the proliferative response of activated CTL clones. Addition of recombinant murine (rm) IL-4 or rhIL-6 alone to the culture failed to influence the response. Also, in combination with rhIL-2, neither rmIL-4 nor rhIL-6 appreciably augmented rhIL-2-supported proliferative response of CTL clones. These studies may provide insights for the development of effective approaches to modulate function and activity of effector T cells.

Immunomodulatory effects of nitrosoureas on the phenotype and functions of T cells in the thymus and periphery

We have recently demonstrated that nitrosoureas such as 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) and chlorozotocin (CLZ) can cure almost 100% of mice bearing LSA tumor, syngeneic to C57BL/6 mice. In contrast, similar or higher doses of streptozotocin (STZ) completely failed to cure LSA-bearing mice. Further studies revealed that the efficacy of nitrosoureas may depend on their immunomodulating properties. In the current study, therefore, we investigated the effect of these nitrosoureas on the immune system of normal mice. Treatment of C57BL/6 mice with 5 intraperitoneal injections of 20 mg/kg body weight of BCNU or CLZ caused an increase in the percentage of CD4(-)CD8- T cells and a decrease in the percentage of CD4(+)CD8+ T cells in the thymus. In addition, such treatment also caused an increase in the percentage of CD4+ T cells without significantly affecting the CD8+ T cells in the thymus. However, when total cellularity of the thymus was studied, BCNU and CLZ were found to decrease the total number of CD4(+)CD8+ T cells without significantly affecting the other subsets. In contrast, similar or higher (100 mg/kg body weight) doses of STZ had no significant effect on the total number and percentages of T cell subsets in the thymus. Also BCNU and CLZ but not STZ treatment caused a 50% decrease in the total number of CD4+ and CD8+ T cells in the spleen. When T cells in the spleens of nitrosourea-treated mice were functionally analysed, it was observed that BCNU and CLZ caused a dramatic decrease in the T cell responsiveness to ConA, anti-CD3 and phorbol myristate acetate plus calcium ionophore stimulation. In contrast, STZ treatment failed to significantly inhibit the T cell responsiveness to these activation signals. Using the accessory cell-dependent and -independent assays, BCNU and CLZ were found to suppress the functions of both T cells and macrophages. Also, addition of growth factors such as IL-1, IL-2, IL-4 and IL-6 failed to reconstitute the defective responsiveness of BCNU- and CLZ-treated T cells and macrophages. Together our data suggest that nitrosoureas have varying immunomodulating properties and this may in turn determine their efficacy in the treatment of cancer.

Chemotherapy of mice bearing syngeneic tumors with 1,3-bis (2-chloroethyl)-1-nitrosourea is effective only in normal, but not in irradiated or nude, mice: role of L3T4+ (CD4+) and Lyt-2+ (CD8+) T cells

We earlier demonstrated that treatment of C57BL/6 mice bearing a syngeneic tumor, LSA, with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resulted in over 90% survival of the mice, and 100% of the cured mice rejected secondary rechallenge with the homologous tumor but not with a heterologous syngeneic tumor such as EL-4. In the present study we investigated whether the host's immune system was also essential for successful chemotherapy with BCNU. It was observed that BCNU treatment was effective only in normal tumor-bearing mice (100% survival) but not in irradiated or nude tumor-bearing mice (0% survival), thereby suggesting that the immune system, particularly the T cells, was essential for effective treatment with BCNU. Since BCNU-cured mice lack demonstrable T suppressor (Ts) cells, these mice were next used as a model to investigate the phenotype of the T cells mediating tumor rejection. It was observed that L3T4+ (CD4+) or Lyt-2+ (CD8+) T cells from BCNU-cured mice could provide significant protection (80 and 40% survival, respectively) in irradiated or nude mice but not in normal mice. It was also observed that BCNU-cured LSA mice elicited tumor-specific delayed-type hypersensitivity (DTH) reaction, while, normal mice or LSA tumor-bearing mice failed to elicit DTH reaction. Also, only L3T4+ but not Lyt-2+ T cells from BCNU-cured mice when adoptively transferred into nude mice could elicit a DTH reaction. The present study suggests that for effective chemotherapy against a syngeneic tumor, with a tumoricidal drug such as BCNU, the presence of L3T4+ and Lyt-2+ T cells in the host is essential.

Adoptive transfer of immunity by spleen cells from LSA-lymphoma mice cured by BCNU

BCNU treatment of advanced LSA lymphoma, a poorly antigenic tumor of syngeneic C57BL/ym mice, produced large numbers of cured mice which were highly immune against further LSA tumor challenges. Spleen cells from cured mice were transferred into normal naive mice in close temporal relationship to the injection of 10(3) LSA cells and showed that during a period of two days before to one day after tumor injection, the MST and per cent tumor takes could be greatly modified. Activity was only weakly present in bone marrow or thymus cells but mixtures of these cells with or without added spleen cells were effective. In 400 rad sublethally irradiated mice it was also found that transferred spleen cells prevented progression of tumor, and resistance was permanent. This indicates that all elements of tumor recognition, affector and effector limbs of immune response were present in the adoptively transferred spleen cell population.